Humans were tossed about like toys as waves travelling at up to 500kms (310miles) an hour, and at heights of 6metres (20 ft) smashed the coastlines of six countries early yesterday morning.
The death toll of 11,300 people, from Indonesia, Sri Lanka, India, Thailand, Maldives and Malaysia – including British tourists – was still rising last night, as people frantically searched for missing loved ones and emergency workers tried to tend the injured, many in make-shift hospitals.
Thousands of fishermen throughout the region are among the missing after boats were seen to be tossed through the air like "paper" by the enormous waves.
And up to 10,000 tourists hoping to celebrate the Christmas period in the sun were among at least a million left stranded without food, shelter or possessions – many having to run for their lives from the beach as the massive tidal wave approached around breakfast time, 1am in Britain.
Holidaymakers watched in horror as some of the world's most beautiful islands were ripped apart by the surge, caused by the 8.9-magnitude earthquake.
In Thailand, the worst-hit areas were on beaches near the resort of Phuket, with reports of divers and sunbathers being swept out to sea. Hotels were under water, after waves up to 20ft high hit the coast, and there were reports of tourist bungalows being carried away by the water.
Tourists spoke of their disbelief at the scale and speed of the disaster.
"I woke up to see a wall of water, trees and cars coming towards us, very quickly," said one survivor.
Phuket hotel worker Boree Carlsson told how the tide of water flooded the hotel lobby and pulled furniture onto the street. "As I was standing there, a car actually floated into the lobby and overturned because the current was so strong."
On the island of Koh Phi Phi, officials spoke of widespread damage and islanders and tourists being airlifted to safety. One report from the island said 200 bungalows had been swept out the sea.
In neighbouring Malaysia, foreign tourists swimming or riding jet skis were among at least 42 people killed at beach resorts on Penang, off the west coast.
Dozens of other locals and tourists have been reported missing from the island and the mainland states of Kedah and Perak, but it is not yet known if any Britons are among the dead.
Tens of thousands of people were temporarily evacuated from high-rise hotels and apartments in Penang and in the capital, Kuala Lumpur.
Nicola Barton, from Croydon, Surrey, was staying in the Paradise Island Resort in the Maldives. She said: "It is just horrific. It is like a war zone. There are wooden sun beds floating round the island, chairs from the restaurants and glass smashed everywhere."
There were horrific scenes in Indonesia, where at least 4,185 people are thought to have died. Most of the dead are believed to be in the northerly-most province of Aceh. Towns were levelled by tidal waves which left bodies wedged in trees as the waters receded, Indonesian officials and witnesses said.
But worst hit was Sri Lanka, where the death toll stands at some 4,500, and a state of emergency has been declared.
Daniel Thebault, from Jersey, was in the south-west. He said: "We were having a late breakfast in our hotel, about 50 yards from the beach, when people sitting near the windows started shouting.
"We heard a roaring noise and could see ripples of frothy water bubbling up fast from the beach. Two or three minutes later, the waves smashed into the hotel, breaking windows and hitting the tables."
Eyewitness Gemunu Amarasinghe, a photographer, added: "I saw people bringing in bodies from the beaches and covering them with sarongs."
BBC reporter Roland Buerk told how he was caught in a tidal wave at a resort in Unawatuna.
"First of all we climbed up into a tree for a couple of minutes, but then that began to fall down because of the water," he said. "We were swept along for a few hundred metres, trying to dodge motorcycles, refrigerators and cars that were coming with us."
In India, the waves swept away boats, homes and vehicles, killing nearly 2,300 people in the southern states of Tamil Nadu, Andhra Pradesh and Pondicherry.
Tamil Nadu's beaches resembled open-air mortuaries as fishermen's bodies were swept ashore, and retreating waters left behind others killed inland. The sea flooded the streets of Cuddalore, flipping over dozens of cars. At least 20,000 people were evacuated from the region.
At least 300 people were killed on India's Andaman and Nicobar islands, and another 700 were missing and believed dead, the region's police chief said. "I was shocked to see fishing boats flying on the shoulder of the waves, as if made of paper," said one Andhra Pradesh resident.
Two children were drowned in neighbouring Bangladesh, as a boat with about 15 tourists capsized in high waves off Kuakata. The fate of the tourists was not known last night.